In a number of different ways it is possible to accomplish a reciprocating movement or force, which it may be desirable to transform into a undirectional movement or force. A relatively recently developed technique is to utilize materials having magnetostrictive properties. Magnetostriction means that a material change its dimensions when exposed to a magnetic field.
Materials with such properties are typically alloys with rare earth metals, an alloy with terbium and iron being available under the name Terfenol. This material Terfenol has a very high magnetostriction, namely up to 0.2% at a magnetic field with a field strength of appr. 3000 oersted, and a very fast response.
Due to the magnetostriction a Terfenol rod exposed to a pulsating magnetic field and prestressed for accomplishing a return to original shape will have a reciprocating length and accordingly exert a reciprocating force.
In order to utilize this oscillating movement or force in a practical force actuator this movement has to be transformed into a unidirectional movement of a push rod or the like in the actuator.